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ORIGINAL ARTICLE
Year : 2020  |  Volume : 10  |  Issue : 1  |  Page : 56-60

Cutting efficiency and dentinal defects using two single-file continuous rotary nickel–titanium instruments


Department of Operative Dentistry and Endodontics, Faculty of Odonto-Stomatology, University of Medicine and Pharmacy at Ho Chi Minh City, Vietnam

Date of Submission20-Apr-2019
Date of Decision19-May-2019
Date of Acceptance11-Jun-2019
Date of Web Publication27-Dec-2019

Correspondence Address:
Dr. Khoa Van Pham
652 Nguyen Trai Street, Ward 11, District 5, Ho Chi Minh City
Vietnam
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/sej.sej_64_19

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  Abstract 

Aim: The aim of this study was to evaluate and compare the cutting efficiency and dentinal defect rates using two single-file continuous rotary nickel–titanium instruments.
Materials and Methods: Thirty-two resin endo training blocks and 48 mesiobuccal roots of extracted human first lower molars were divided into five groups (16 for each group). Roots were checked for the homogeneities of root canal dimensions, thickness of dentin walls, and curvatures using images of X-ray radiographs on AUTOCAD software. Two groups of resin blocks and two groups of mesiobuccal canals were instrumented using two continuous rotary nickel–titanium instruments (Neoniti A1 and OneShape), the remaining group (control group) of mesiobuccal canals was left intact. The cutting efficiencies of instruments were quotients of the loss weights of specimens, and the time needed for instrumentation. ANOVA and post hoc Tukey tests were used to analyze the differences among the experimental groups. The cracks on the sectioned root surfaces at 3-, 6-, and 9-mm levels were recorded. Fisher exact test was used to analyze the differences among the experimental groups.
Results: Cutting efficiency of OneShape was greater than that of Neoniti on both resin and human root canals (P < 0.05). There was no significant difference between dentinal defects created at different levels of canals by two kinds of nickel–titanium instruments (P > 0.05).
Conclusions: OneShape instrument was more efficient than Neoniti on both kinds of root canals. Both instruments created dentinal defects on root canal walls.

Keywords: Cutting efficiency, dentinal defect, nickel–titanium, rotary, single file


How to cite this article:
Pham KV, Nguyen NQ. Cutting efficiency and dentinal defects using two single-file continuous rotary nickel–titanium instruments. Saudi Endod J 2020;10:56-60

How to cite this URL:
Pham KV, Nguyen NQ. Cutting efficiency and dentinal defects using two single-file continuous rotary nickel–titanium instruments. Saudi Endod J [serial online] 2020 [cited 2020 Apr 2];10:56-60. Available from: http://www.saudiendodj.com/text.asp?2020/10/1/56/274193


  Introduction Top


Preparation is one of the most important stages in endodontics, including the biochemical and mechanical ones. Although these two purposes of this phase cannot be separated, mechanical instrumentation still plays an important role in whole endodontic therapy.[1] Biomechanical preparation nowadays was completed by many ways, but the most popular one was via rotary nickel–titanium instruments.[2] There are many nickel–titanium instruments systems on the market today, and they are continuously improved in many aspects, including designs, materials, and modes of rotary. The manufactures incessantly innovate for their own products to reduce the time needed, complexity in use, fatigue of clinicians, and therefore, increasing the success rate in the clinical setting of these instruments. In efforts to reach those goals, the single-file instrument systems were produced with two modes of rotary: reciprocating and continuous rotary. One of the first reciprocating single-file systems for root canal preparation was WaveOne (Dentsply, Maillefer, Ballaigues, Switzerland) with many advantages.[3] Recently, some manufacturers developed the new single-file systems using continuous rotary with different cross-sectional surfaces (OneShape – Micro-Mega, Besançon, France)[4] and special surface treatments (Neoniti – Neolix, Châtres-la-Forêt, France).[5] The single-file systems not only assisted to reduce the number of instruments needed for instrumentation to one or two instruments but also helped the clinician need less time for preparation and decreased the operator's fatigue.[6] Along with the new features in designs or in treatment processes, these new continuous rotary single-file systems needed small torque values when used in the root canals. The low torque values enhanced the safety of the rotary instruments in root canal preparation; and however, this raises some questions for efficiency and drawbacks of the instruments. Whether or not the new instruments can maintain their cutting efficiencies to gain the optimal results using that low torque values. One different concern was the ability of creating the dentinal defects of these new instruments. The reciprocating instrument demonstrated that it could make defects on the dentine wall,[7] so whether or not the continuous rotary single-file instrument systems can create defects on the root canal wall. The aim of this study was to evaluate and compare the cutting efficiency and dentinal defect rates using two continuous rotary single-file nickel–titanium instruments.


  Materials and Methods Top


The present study was approved by the Research Ethics Committee of the University of Medicine and Pharmacy at Ho Chi Minh City, Vietnam (#1670/QĐ-ĐHYD). A total of 32 L-type resin endo training blocks (ETBs) (Dentsply, Maillefer, Ballaigues, Switzerland) and 48 extracted human first lower molars that had minimum 10-mm length of, intact, two separated canals in, crack-free and nonprevious root canal treatment mesial roots were used for the present study. Distal roots of these molars were cut and discarded. Teeth then were accessed using Martin and Endo-Z burs (Dentsply, Maillefer, Ballaigues, Switzerland). Mesial canals were located and negotiated to the apical foramen using ISO 10 and then 15 K-files (Dentsply, Maillefer, Ballaigues, Switzerland). The teeth with an ISO 15 K-files in mesiobuccal canals were radiographed in buccolingual and mesiodistal directions with a lead grid of 1 mm × 1 mm square. Radiographs were scanned into the computer and analyzed using AutoCAD 2017 (Autodesk, San Rafael, CA, USA). Root canal curvatures were determined using the Schneider concept [8] and the thicknesses of dentinal walls at 3-, 6-, and 9-mm levels of each canal (in both directions on radiographs) were measured using the Bose technique.[9] This step was conducted to determine the homogeneity of groups of teeth used in the study about the root canal curvatures of mesiobuccal canals (from 25° to 70°) and the dimensions of root canals. The teeth were divided into three equal groups so as to these three groups had similar root canal curvatures, root canal widths, and dentinal wall thicknesses. Group 1 was control group and was not instrumented. Groups 2 and 3 were used for Neoniti and OneShape preparation. A total of 32 ETBs were divided into two equal groups, Groups 4 and 5 used for Neoniti and OneShape preparation. Before starting the root canal preparation for the groups, specimens' weights were measured using AUW220D scale at 1/105 exact level (Shimadzu, Kyoto, Japan). Groups 2 and 4 were instrumented using Neoniti A1 in the WaveOne Endo Motor (Dentsply Maillefer, Ballaigues, Switzerland) with manufacturer's parameters (1.5 N.cm and 300 rpm). Groups 3 and 5 were instrumented using OneShape in the WaveOne Endo Motor with the manufacturer's parameters (2.5 N.cm and 300 rpm). Hyposol – 3% hypochlorite sodium (Prevest DenPro, Digiana, India) was used as irrigation for preparation. Each instrument was used for a maximum of three root canals or three ETBs. The actual time needed for root canal instrumentation was recorded for each specimen using an ADANAC 3000 watch at 1/102 exact level (Marathon Watch, USA). This time did not include the instrument cleaning time and irrigation time. The specimens were weighed using the AUW220D scale after instrumentation. The cutting efficiency was the result of the division of loss of specimen's weight for the root canal preparation time. After instrumentation, all coronal parts of specimens in Groups 1, 2, and 3 were embedded into clear acrylic resin Perma-cryl CF (GC America Inc., Alsip, IL) using a wood mold. Roots of specimens were cut at 3-, 6-, and 9-mm levels perpendicular to the root's long axis at that points using low-speed saw Buehler Isomet (Buehler, Lake Bluff, IL, USA). Images of all slices were captured using the camera DP25 of the stereomicroscope Olympus SZX16 (Olympus Corporation Ltd, Tokyo, Japan) at magnification of 25 times and stored in the hard drive using software Olympus cellSens Standard (Olympus Corporation Ltd, Tokyo, Japan). Images were evaluated by independent observers to detect dentinal defects as complete crack, incomplete crack, and craze line [Figure 1]. Data were analyzed using SPSS version 20.0 (IBM, Armonk, NY, USA).
Figure 1: Complete crack at the distal aspect of the mesiobuccal canal of mandibular first molar after root canal preparation

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  Results Top


The mesiodistal and buccolingual dimensions of mesiobuccal canals for Groups 1, 2, and 3 at 3-, 6-, and 9-mm levels were displayed in [Table 1]. There were no significant differences among three groups about these dimensions (P > 0.05).
Table 1: The mesiodistal and buccolingual dimensions (mm) of root canals for three groups at three levels (mean±standard deviation)

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The thicknesses of root canal walls of roots for Groups 1, 2, and 3 at 3-, 6-, and 9-mm levels in mesiodistal and buccolingual directions were displayed in [Table 2]. There were no significant differences among three groups about these dimensions (P > 0.05).
Table 2: The thicknesses (mm) of root canal walls of roots for three groups at three levels in mesiodistal and buccolingual directions (mean±standard deviation)

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Time amounts needed for root canal preparations of four experimental groups were illustrated in [Table 3]. There were significant differences between time amounts needed for instrumentations using Neoniti and OneShape, with time amounts for Neoniti were longer than that for OneShape on both extracted human root canals and ETBs (P < 0.05). Neoniti needed more time to prepare the ETBs than it needed to prepare the human dentin canals (P < 0.05). However, there were no significant differences between time needed for preparation using OneShape on both human dentin and resin (P > 0.05).
Table 3: Time amounts (seconds) needed for root canal instrumentations of four groups

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The cutting efficiencies of two instruments were displayed in [Table 4]. Neoniti was less efficient than OneShape when used on both human dentin roots and ETBs. Both instruments were more efficient on human dentin canals than on ETBs (P < 0.05).
Table 4: Cutting efficiencies (log10 [mcg/s]) of two experimental instruments

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The unit of cutting efficiency was mcg/s. However, the data were transformed using the function log10 (logarithm with the base of 10) to gain the normality of distribution.

The number of dentine slices with dentinal defects was displayed in [Table 5]. There was no significant difference between the two experimental groups (Groups 2 and 3) prepared using two instruments (P > 0.05).
Table 5: Numbers and rates of dentin slices with dentinal defects for two groups of root canals prepared using two instruments

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Correlation between cutting efficiency and dentinal defects was displayed in [Table 6]. All P values were >0.05, and therefore, there was no correlation between the cutting efficiency of the different instruments and dentinal defects created by these instruments in this study.
Table 6: Correlation between cutting efficiency and dentinal defects

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  Discussion Top


The resin ETBs were used for this study due to its identical canal shapes, although its Knoop hardness was lower than that of human dentine (22 kg/mm 2 vs. 40 kg/mm 2).[10],[11] Extracted human tooth was a different story. Although the utilization of a human tooth provided a real situation, the differences in canal shapes could affect the result. Therefore, teeth were chosen and checked for the homogeneity of mesiobuccal canal dimensions and mesiobuccal root dentine thicknesses. The periapical radiographs in two directions with the lead grid next to the tooth on the radiograph using the AUTOCAD seemed appropriate for this study. Because of the complexity of the root canal systems in mesial roots, only mesial roots with two separated canals and foramen were chosen for this study. The mesiobuccal canal was chosen for this study because this canal curvature was greater than mesiolingual one, and there were limited data about the dentinal defects created by rotary instruments on this canal.[12],[13]

In the manufacturers' instructions, preflared instruments were used before the main instruments, Neoniti C1 for Neoniti and One G for OneShape. However, these instruments possessed large volumes and great tapers, and therefore, these instruments could create dentinal defects before the main instruments were used.[14] To reduce bias, Neoniti C1 and One G were not used, and the canals were only prepared using Neoniti A1 and OneShape for corresponding groups. Multiple uses of nickel–titanium rotary instruments were not recommended by manufacturers nowadays, although there was study reported that some certain instruments could be used up to five canals without considerable metallurgical characteristics.[15] The number of canals prepared by one instrument in this study was similar to that of a previous study [16] and less than in other study.[17]

Time needed for preparation was calculated only for actual working time of instrument in canals, not including the cleaning time and irrigation time in this study. This way of time calculation for preparation was not similar to that of a previous study;[18] however, the results of both studies were similar with the time needed for preparation using Neoniti being greater than that of OneShape.

The cutting efficiency measured by calculating the loss weight of material over a unit of time was still a reliable method.[19] This way was used in the present study and was not similar to the method of a previous study,[18] in that, only extruded materials over the apical foramen were measured. The working time of OneShape for ETBs was longer than that for human root canals; however, this difference was not significant. This result proved that OneShape retained its cutting efficiency even through ETBs, and this might be due to the special designs of this instrument with appropriate changes along the root long axis as well as electropolishing procedure.[4] The better cutting efficiency of OneShape when compared to that of Neoniti showed that Neoniti's high flexibility and low torque might be the causes. The result of this study showed that, although possessing the lower Knoop hardness, ETBs seemed harder to be instrumented when compared to human root canals. One of many reasons might be due to the fusible characteristic of resin when subjecting to the friction created by the instruments. This increased friction and reduced considerable cutting efficiency of the instruments. This issue should be noted in both endodontic research and training.

Dentinal defects still presented in the control group of the present study. These defects might be due to manipulation in the extraction procedure. Under micro-CT investigation, there still were dentinal defects in extracted human roots due to many reasons.[12] Dentinal defects in both experimental groups were higher than that in control group; however, this difference was not significant in the present study. This showed that both experimental instruments created no more considerable dentinal defects on mesiobuccal root canals. Neoniti instruments created more dentinal defects than ProTaper Universal,[20] ProTaper Universal made more dentinal defects than ProTaper Next,[21],[22] and ProTaper Next produced more cracks than OneShape.[23] From these results, it seemed Neoniti created more dentinal defects than OneShape did. The result of the present study confirmed that, however, this difference was not significant. This might be explained by asymmetrical square design of Neoniti [20] and more appropriate designs of OneShape for each part of root canals.[23]

There was no correlation between the cutting efficiency of an instrument and dentinal defects created by instruments might be due to a small sample size. This correlation should be investigated in future research.


  Conclusions Top


OneShape was more efficient than Neoniti on both kinds of root canals. Both instruments created dentinal defects on root canal walls. There was no correlation between cutting efficiency and dentinal defects in this study.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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    Tables

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